1. Field of Invention
The invention is related to a reconfigurable switched-capacitor input circuit, and more particularly, to a reconfigurable switched-capacitor input circuit with digital-stimulus acceptability for testing mixed-signal circuits.
2. Description of the Related Art
At all electronics and electrical manufacturers focus on the family amusement market of meanwhile, makes the audio chip market growing up significantly. Hence, the test for a mixed-signal component that is comprised of the switched-capacitor circuits, such as the Sigma-Delta modulators, becomes more and more important. The evolution of the integrated circuit manufacture technology allows integrating diverse components such as digital, analog, and memory circuits on the same chip. The testability and high testing cost of such products become a sever issue due to the diversity of the test characteristics of the embedded circuits. And this issue is much more critical for the mixed-signal circuits since their tests traditionally have to rely on high-priced mixed-signal circuit testers like Aglient 94000. Also, on account of most testers that do not support testing the analog circuit and digital circuit simultaneously, a longer testing time is required and makes disadvantageous fluctuation factors in both of the cost and time-to-market of the products.
U.S. Pat. No. 5,132,685 titled as “Built-in self test for analog to digital converters” indicates that a ramp generator with a large area is exerted additionally and provides a ramp voltage to the A/D input, while a state machine monitors the output. Nevertheless, the testing accuracy depends on how accurate the ramp generator's output is and the generated ramp signal is not suitable for testing the circuits of either the Sigma-Delta modulator or the filter.
As for what disclosed in U.S. Pat. No. 5,305,003, “Test device of analog/digital converter”it is a digital circuit for testing the analog/digital converter only and fails to test the analog circuit.
In U.S. Pat. No. 5,659,312, it titles as “Method and apparatus for testing digital to analog and analog to digital converters” and reveals that a highly accurate built-in digital-to-analog converter with a large area is used as the stimulus source. In this invention, the testing accuracy depends on the accuracy of the built-in digital-to-analog converters exerted; that is, the digital-to-analog converter has to be verified by some means first. Consequently, higher cost for hardware and testing has to be endured.
A built-in self-test for analog to digital converter is mentioned in U.S. Pat. No. 6,333,706, a built-in random-waveform generator with a large area is applied in this invention. Still, the accuracy of test results depends on the accuracy of the built-in random-waveform generators employed. In addition to the higher hardware cost, the built-in random-waveform generator would not carry out the at-speed tests.